Re: Builtin test and parsing of conditionals

[Peter Stephenson <p.stephenson@samsung.com>]

On Wed, 04 Sep 2013 09:15:03 -0700
Bart Schaefer <schaefer@brasslantern.com> wrote:
> According to some discussion on the austin-group (POSIX) mailing list,
> the following:
> 
> 	test ! -a !
> 	test ! -o !
> 	test ! = !
> 
> should all be parsed as comparing the string "!" to the string "!", but
> zsh gets this right only in the last case.

I don't understand that.  -a means "and" and -o means "or", unless
they're being interpreted as strings, but I don't see how that could be
if ! is supposed to be interpreted as a string.   So where does the
implicit comparison come from?  If -a were taken as high precedence you
might read it as

test -n ! -a n !
test -n ! -a n !

which is how

test foo -a bar
test foo -o bar

are interpreted, which you can see by

test foo -a '' # false
test foo -o '' # true

... same if you omit the ''.

(Outside our control, but I imagine people aren't daft enough to rely on
this sort of behaviour in new scripts...?)

pws